Field of Invention
The invention relates to the field of containers, particularly bottles or jars, manufactured by blow molding or stretch-blow molding from parisons of plastic material such as polyethylene terephthalate (PET).
Description of Related Art
A container generally comprises an open neck, through which the contents (ordinarily a liquid) are introduced, a body, which imparts to the container its volume, and a bottom, which closes the body opposite the neck and forms a base intended to ensure the stability and the support of the container when it rests on a surface.
Containers intended for carbonated beverages, in which the pressure of the gas dissolved in the liquid causes considerable mechanical stresses, are predominantly provided with large-height bottoms with a petaloid shape: the bottom comprises projecting feet, in the shape of petals, separated by convex wall portions, called hollows or valleys, which extend radially from a central zone of the bottom. The feet, of large height (i.e., in a ratio of about 1/2 with the diameter of the container), are intended to ensure the support of the container placed on a surface; the valleys are intended to absorb the forces (thermal, mechanical) exerted by the contents. An illustrative example of this type of bottom will be found in the international application WO 2012/069759 (SIDEL).
The petaloid-shaped bottom appears as a relatively successful solution exhibiting a good resistance to the strong internal pressures in the container (particularly as a result of the hemispherical shape of the valleys).
However, the petaloid-shaped bottom requires a considerable amount of material (a 0.5 l container with a standard petaloid-shaped bottom having a weight that is greater than or equal to about 18 g), as well as a relatively high blow molding pressure (on the order of 22 to 30 bars), to ensure a proper impression-taking of the feet and valleys.
These constraints tend to disqualify the petaloid-shaped bottom for flat-liquid-type applications (typically table water or non-carbonated beverages), for which both the blow molding pressure and the amount of material used (today on the order of 10 g at most for a 0.5 l container) are minimized.
It is becoming common for certain applications of flat liquids that are susceptible to oxidation (particularly fruit juices, but also certain plain waters) to remove the air above the flat liquid and to replace it with an inert gas (typically nitrogen). In practice, this operation is performed by adding a drop of liquefied inert gas to the surface of the flat liquid, immediately preceding the capping of the container. This operation causes an excess pressure in the container. Although seemingly slight (on the order of 0.5 to 1 bar), this excess pressure is enough to considerably increase the stresses that are exerted on the bottom, without, however, these stresses justifying the return to standard petaloid-shaped bottoms (i.e., of large height).
Now, a bottom provided with a simple concave arch, if it a priori meets the requirements of savings of material and of easy blow moldability, is not, however, able to support without significant deformation the stresses due to the doubled hydrostatic pressure of the pressure of the added neutral gas.